Polymeric, metallic, and metalized polymeric films have various properties that make them useful as packaging or labeling materials. For example, such films may be lightweight, strong, impervious to liquids and gases, transparent, printable, foldable, fusible, and/or heat-shrinkable. Films are commonly formed into sheets and rolled for processing, transport, and storage.
Films may be printed with various inks to provide information, decoration, etc. For example, rolls of polymeric films may be printed by unrolling the film, subjecting the unrolled film to a corona treatment (surface modification by exposure to a low-temperature plasma), applying an ink to the treated film, and rolling the film to another roller. Printing typically occurs in high-speed printing machinery, which may be capable of processing 100 linear feet per minute of plastic film or more.
Errors in printing (e.g., typographical errors in labels, overruns, alignment errors, incorrect colors, etc.) can be costly because large quantities of film may be processed before an error is identified and printing is interrupted. Higher-speed printing equipment is desirable in the industry because it allows for higher outputs; but higher-speed printing may correspond to larger quantities of misprinted films when errors are made. Misprinted films are typically sold as scrap for a small fraction of the price of virgin film. Such films may be melted and recycled, but this process may be costly and environmentally problematic.
Various attempts have been made to develop methods of effectively removing ink from films. For example, European Patent Specification EP 1 414 829 A1, published May 19, 2004, and entitled “Procédé de recyclage de support d'impression imprimé de type film plastique et installation pour la mise en oeuvre dudit procédé,” describes a de-inking process in which a plastic film is simultaneously or sequentially immersed in a detergent composition and scrubbed with brushes. International Patent Application Publication WO 95/09256, published Apr. 6, 1995, and entitled “Treatment of Surfaces by Corona Discharge,” describes a surface-cleaning process that may be used for metallic sheets or foils. An electric discharge is used to remove grease or oils from such metallic films. International Patent Application Publication WO 2006/028263 A1, published Mar. 16, 2006, and entitled “Erasable Ink, Method of Erasing Image Including the Same, and Method of Recycling Recording Medium Using the Erasing Method,” describes an erasable ink that may be printed onto a recording medium. The ink may be removed from the recording medium by exposure to an oxidizing gas, such as that generated by a corona discharge. The entire contents of each of these documents are hereby incorporated by reference.